Conventionally, various methods of determining whether knocking (knock) is present or absent have been proposed. For example, there is a technique of determining occurrence of knocking based on whether or not magnitude of vibration detected in an internal combustion engine is greater than a knocking determination value. A knock control device for an internal combustion engine disclosed in Japanese Patent Laying-Open No. 2003-021032 includes: a knock sensor detecting knocking in an internal combustion engine; a statistical processing portion statistically processing an output signal detected by the knock sensor; a first temporal determination portion determining occurrence of knocking based on a processing result by the statistical processing portion; a second temporal determination portion determining occurrence of knocking based on a waveform shape of the output signal detected by the knock sensor; and a final determination portion finally determining occurrence of knocking based on the knock temporal determination of the first temporal determination portion and the knock temporal determination of the second temporal determination portion. When both of the first and second temporal determination portions determine that knocking has occurred, the final determination portion finally determines that knocking has occurred.
According to the knock control device disclosed by the publication, a knock temporal determination by a statistical processing program and a knock temporal determination by a waveform shape program are used, and only when both of the temporal determinations determine that knocking has occurred, it is finally determined that knocking has occurred. As a result, occurrence of knocking can precisely be determined even as to an output signal, which has been erroneously determined by a knock determination employing solely the statistical processing program or the waveform shape program.
Meanwhile, in an internal combustion engine, besides vibration due to knocking, vibration may occur when an intake valve or an exhaust valve sits on its seat. Vibration may also occur due to the actuation of an injector (in particular, an in-cylinder direct injector that directly injects fuel inside a cylinder) or a high-pressure pump that supplies fuel to the injector. When such vibration is detected as noise together with vibration due to knocking, the detected waveform is different from that at the time of knocking, even though knocking has occurred. In this case, if whether knocking is present or absent is determined based on the waveform shape as in the knock control device disclosed in Japanese Patent Laying-Open No. 2003-021032, it may erroneously be determined that knocking has not occurred, even though knocking has occurred.